Composition for stripping durable, adherent coatings



United States Patent 3,391,085 COMPOSITION FOR STRHPING DURABLE, ADHERENT COATINGS Joseph T. Crockett, Aberdeen, Md., assignor to the United "ice chloride and formic acid solution has been appreciated for some time, the water content which could be successfully incorporated by simple mixing to form a single phase solution has been relatively low. Further additions States of America as represented by the Secretary of of water separated into liquid phases without contributthe Army ing any noticeable effects.

N0 Drawiligcontinuatibn'ifljpal't ap'liilcatlon Mixtures of methylene chloride, formic acid and water 318,452 1963' This application 1965 were known to possess stripping action on various paints; 2 S (Cl 252 143) however, these mixtures were not found to be successful mm for removing phenolic epoxide of the type specified in the The invention described herein may be manufactured aforementioned Military Specification. The effectiveness and used by or for the Government for governmental of the present composition which includes both phenol purposes, without the payment to me of any royalty and p-toluenesulfonic acid is very unexpected and subthereon. stantially greater than for similar compositions that do This application is a continuation-in-part of application not contain these ingredients, even when water is included Ser. No. 318,452, filed Oct. 23, 1963, for Paint Stripper therein at comparable levels.

p-Toluenesulfonic Acid Modified, now abandoned. The combined use of phenol and p-toluenesulfonic acid This invention relaltes to an improved stripping comresults in several-fold increase in the water that may be position which is useful for removing various types of combined and retained therein as a one-phase solution.

paints and related coatings. More specifically, it relates The water content may be desirably raised to levels of to a composition which displays substantial stripping bctWeen 10 and 20 percent by weight of the composition. action with the more durable, adherent epoxy type coat- Moreover, the addition of phenol within the limits disings that defy similar strippers of the prior art. closed herein serves both as an emulsifier for the water Military requirements have prescribed for a single and as a solubilizer for the disintegrating coating. The stripping composition which will be eifective for loosening inclusion of pl en sulfonic acid enables the water to dry paint and other finish coatings from nearly all surfaces. be dispersed readily y simpis mixing of the ingredisnts;

In addition to a more universally applicable pain it is also an active compound of a molecular structure mover, the desired composition should also be quickthat is capable of y Penetration When Carried y a acting and capable of penetrating and loosening a coating vehicle. The preferred range of p-toluenesulfonic acid in without scraping or rubbing so that the loosened coatthe Present Composition is about Percent y Weighting may be washed away in a tream of ater, The prob- Theoretical aspects Of the present composition attribute lem posed by military exigency is to conc ufthe rapid penetration and disintegration of a coating to ficient softening and penetrating action in a single comthe fact that the disintegration Products become hydrogen position for not only conventional paints b0fldd t0 thfi P1161101 and thfi bol'ldfid pI'OduCts, therefore, lacquers, enamels, resins, etc., but also the more durable, become soil-ibis in methylene chlorideh rem val of adherent coatings that are highly resistant to softening the reaction Products y methyififle Chloride i du s a action. further attack by the formic acid on the remaining In accordance with the above requirements, an irncoatiligproved stripping composition is now provided which has In the following table, Examples are lustrative been f d to b emcient i loosening various paints of the present invention and demonstrate their ability to and related films from their supporting surface. The remove a baked, Pigmented Phelioiic epoxide gessence of the invention is predicated on an improved The tests W Performed on steel Panels hi h Were oft i g and penetrating action as displayed by the sprayed with the test phenolic epoxide and then baked instant composition in a stripping test involving a high at 420 F. for 20 minutes. The coating consists of the resistant phenolic epoxide coating. The particular phenolic type III heat'ha Tdenab1e bisphenol P idB and phenolepoxide used in demonstrating the effectiveness of the formaldehyde mixture which is Pigmented With powdered present composition is amixture of bisphenol epoxide and aluminum, ALCOA #422, at about 22-25 P n y phenol-fonnaldehyde i as di l d i Mili weight of the final mixture. The durability and adherence Specification MlL-V-12276A, pigmented with aluminum of this baked Coating y be appreciated from tho fact powder and th coating is bak d bo 400 F, fo that it is intended for use on metal which is deformed or twenty minutes. fabricated after it is coated.

Examples -1 2 3 4 5 6 7 8 9 10 11 Ingredients, Weight Percent Methylene Chloride 85.14 80.68 70.32 60.41 48.19 25.21 7.93 71.93 62.47 50.25 72.26 Formic Acid 9.28 8.75 7.61 6.96 5.25 2. 73 .88 7.78 7.20 5. 47 7.84 Phenol 3.23 6.62 12.68 18.70 23.18 27. 30 22. 94 12. 97 19. 34 24.17 0 Water content 1.83 2.97 7. 38 10. 92 19.70 40. 42 64. 57 7. 32 1 99 2011 11190 p-Toluenesull'onic acid. 52 1. O3 2. 01 3. 01 3. 68 4. 34 3. 68 0 0 0 0 Percent paint removed 5 66 90 100 100 None None None None None Broadly stated, the present composition comprises a The percent of paint removed was determined from the mixture of methylene chloride, formic acid, phenol and amount of paint bli-stered from a 25 mm. circle on a panel p-toluenesulfonic acid which is capable of incorporating coated at 1 mil thickness with the aluminum-pigmented and retaining therein a substantial amount of water in phenolic epoxide which Was baked at a temperature over a single phase solution. Formic acid is employed in the 400 F. for 20 minutes.

composition as the principal activator of methylene chlo- As standards of comparison, Examples 8-11 demonride to increase the stripping action. A high water constrate the ineffectiveness of similar compositions in which tent, which is readily obtainable as a result of the present Water was added in sufiicient amounts for test purposes. invention, contributes to the softening and penetrating In the absence of p-toluenesulfonic acid, these composiproperties of the composition and thus provides for effections were found to be ineffective against the test coating.

tive disintegration of a more durable, adherent coating. Although the essential role of water in a methylene Examination of the data in the table indicates that Examples 4 and 5 are the most effective compositions in accordance with the invention; Examples 2, 3 and 6 indicate the range of etfectiveness. In Example 1. the 452% p-toluenesulfonic acid, while not really effective, has begun to show signs of stripping activity. Even though there is a high enough concentration of p-toluenesulfonic acid in Example 7, there is an insufiicient vehicle present to carry it through the surface of the coating.

An effective range of ingredients by weight percent is as follows:

Methylene chloride U-7l Formic acid .l-ti Water content .i-20 Phenol 12-30 p-Toluenesulfonic acid 1- Since the stripping composition is acidic. it is advisable not to apply it to coated, basic metallic surfaces and it is preferable to include an inhibitor in the composition when applying it to ferrous metals. Aluminum is not afiected by this stripper. Investigation has shown that corrosion to ferrous metals resulting from contact or immersion in the present composition can be prevented by adding a 37% solution of formaldehyde (formalin) in about 1% by volume of said composition.

The time necessary for complete removal of the test scribed and certain specific examples have been given by way of illustration but no limitation is intended thereby, the spirit and scope of the invention being limited only by the terms of the appended claims.

What is claimed is:

11. A stripping composition consisting essentially of the following ingredients in the proportions by weight specified:

ingredients Percentage by weight Methylene chloride 40-71 .Formic acid 28 lPhenol 12-30 Water 3-20 p loluenesulfonic acid 1-5 :2. A stripping composition in accordance with claim 1 in which water is present in an amount in the range of about 10 to 20 percent by weight.

3. A stripping composition in accordance with claim 1 in which p-toluenesulfonic acid is present in an amount in the range of about 2 to 4 percent by weight.

t. A stripping composition in accordance with claim 1 which includes formalin as a corosion inhibitor in about 1% by volume of said composition.

References Cited iJNITED STATES PATENTS 11,470,225 10/1923 Holmes 252-146 1083.013 5/1937 Freeman 252-143 X 11,507,984 5/ 1950 Kuentzel 252-143 3,072,579 11/1963 Newman 252-443 3,075,923 i/ 1963 Berst et a1 252--143 X lLEON D. ROSDOL, Primary Examiner. W. E. SCHULZ, Assistant Examiner. 

1. A STRIPPING COMPOSITION CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS IN THE PROPORTIONS BY WEIGHT SPECIFIED: 